1. Field of the Invention
The present invention relates generally to optical systems and, more specifically, to an apparatus for positioning optical components, such as those used in optical communications systems.
2. Background Information
With the increasing popularity of wide area networks (WANs), such as the Internet and/or the World Wide Web, network growth and traffic has exploded in recent years. Network users continue to demand faster networks and more access for both businesses and consumers. As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.
An alternative to present day hardwired or fiber network solutions is the use of wireless optical communications. Wireless optical communications utilize point-to-point communications through free space and therefore do not require the routing of cables or fibers between locations. Thus, wireless optical communications are also known as free space or atmospheric optical communications. For instance, in a free space optical communication system, a beam of light is directed through free space from a transmitter at a first location to a receiver at a second location. Data or information is encoded into the beam of light, and therefore, the information is transmitted through free space from the first location to the second location.
An important aspect of a free space optical communications system is tracking. In particular, it is important that the optical communications beam (e.g., laser beam) is aimed properly from the transmitter at the first location and that the receiver at the second location is aligned properly to receive the optical communications beam. For example, assume that a transmitter is mounted on a first building and that a receiver is mounted on a different second building. Assume further that there is a line of sight between the transmitter and receiver. It is important for the transmitter on the first building to be configured to accurately direct or aim the optical communications beam at the receiver on the second building.
Tracking is utilized for maintaining the alignment of the optical communications beam between the transmitter and receiver in various situations or disturbances. Examples of these various situations or disturbances include the swaying of the buildings due to for example windy conditions, vibration of the platforms on which the transmitter and/or receiver are mounted, atmosphere-induced beam steering, etc. If the tracking system is unable to compensate for disturbances, the optical communications beam is no longer properly aimed at the receiver and, consequently, communications between the transmitter and receiver are lost or impaired.
The present invention provides an apparatus for positioning an optical component, such as a lens or reflector. Positioning of the optical component is facilitated by an adaptive support that is coupled to the optical component on one end, and secured to a generally static structure, such as another optical component or base, at an opposing end. The adaptive support comprises a flexible support member on which a plurality of piezoelectric elements are mounted. In response to differential voltages applied to selected piezoelectric elements, localized portions of the flexible support member are caused to extend and contract. As a result, this localized extension and contraction alters the configuration of the adaptive support such that the orientation and/or position of the optical component are changed.
According to one embodiment, the adaptive support is used to couple a primary reflector to a secondary reflector, wherein the reflectors are arranged in an off-axis Cassegrain reflective collector configuration. By applying controlled differential voltages to selected piezoelectric elements, the apparatus enables the focal point of the collector to be maintained at a desired location, thereby providing compensation for changes in the direction and/or location of an incoming signals, and compensation for physical variations in the optics (e.g., due to temperature changes) of the collector. Similarly, the apparatus enables the direction of outgoing signals to be controlled such that they may be directed toward a desired target location. In this embodiment, the flexible support member has a configuration similar to a section of a truncated cone when coupled to the primary and secondary reflectors, and has a truncated pie-shaped configuration when in a xe2x80x9cflattenedxe2x80x9d condition. In addition, the piezoelectric elements are configured in a radial array when the flexible support member is flattened. As a result, the adaptive support functions as a plurality of flexible struts that are connected between the primary and secondary reflectors, whereby the length of the struts can be altered by selectively applying differential voltages to piezoelectric elements corresponding to those struts. In one embodiment, the flexible support member comprises a printed circuit board that includes a plurality of electrical traces that enable input voltages supplied at a connector to be routed to appropriate piezoelectric elements. To facilitate bending, the printed circuit board includes a plurality of radial perforations. Alternatively, a flex-circuit of similar configuration may be used.
According to other aspects of the invention, a control system is provided for controlling the orientation and/or position of the secondary reflector relative to the primary reflector. In one embodiment, the control system provides a lookup table that enables orientations and/or positions that are stored in the lookup table to be attained by providing appropriate differential voltages to selected piezoelectric elements based on entries in the lookup table corresponding to the row that contains the orientation and position entries. In one implementation of the control system, an acquire mode is facilitated by the lookup table, whereby an incoming or outgoing optical signal can be acquired by moving the secondary reflector to a desired orientation and position based on data in the lookup table. According to further aspects of the control system, a closed loop feedback scheme is provided that enables the control system to implement a tracking mode, whereby a maximal signal strength for an incoming or outgoing optical signal is maintained through fine adjustments of the orientation and position of the secondary reflector.